1. Technical Field
The present invention relates to a technique for driving a light emitting element such as an organic EL (Electroluminescence) element.
2. Related Art
A light emitting device is known in which the driving transistors control the driving current supplied to the light emitting elements. The light emitting device has a problem of an error (deviation from a target value or variation among the elements) in characteristics of the driving transistors. Japanese Unexamined Patent Application Publication No. 2007-310311 discloses a technique that compensates for errors (which may further include an error in an amount of the driving current) in mobility and threshold voltages of the driving transistors by sequentially executing a compensation operation and a recording operation on the pixel circuits of a selected row by a scanning line driving circuit for each horizontal scanning period. The compensation operation is an operation for making the voltage across each holding capacitor, which is interposed between a gate and a source of the driving transistor, approach asymptotically to a threshold voltage by controlling the driving transistor to be in an ON state and subsequently supplying a predetermined reference potential to the gate of the driving transistor from a signal line. The recording operation is an operation for changing the voltage of both ends of the holding capacitor into a voltage according to a gradation level by supplying a gradation potential according to the gradation level to the gate of the driving transistor from the signal line.
Meanwhile, considerable time is needed to make the voltage of both ends of the holding capacitor approach sufficiently to the threshold voltage of the driving transistor by using the compensation operation. However, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 2007-310311, one signal line is used for both operations of supplying the reference potential and supplying the gradation potential. Thus, it is required to complete the compensation operation and the recording operation within a horizontal scanning period in which one scanning line is selected. This causes a problem in that a time for compensation operation is not sufficiently secured. When the time for the compensation operation is insufficient, it is difficult to make the voltage of both ends of the holding capacitor approach sufficiently to the threshold voltage of the driving transistor. Accordingly, it is difficult to effectively compensate the error in the threshold voltage of the driving transistor. On the other hand, when the horizontal scanning period is set to a time that is sufficient to make the voltage of both ends of the holding capacitor approach the threshold voltage of the driving transistor, another problem arises in that an increase (an increase in resolution) in the number of the scanning lines is restricted.